Evergreen Content
Having already discussed short term content as anything that is relevant for less than one year it's time to focus on long term content. This content is typically referred to as evergreen content because it never goes out of date. Year after year these pages should continue to provide you traffic as searchers ask the same question and land on the evergreen page where you provide the answer.
Importance for SEO
Evergreen content provides valuable landing pages for SEO efforts. All of your most desirable, high traffic terms should have a page focused entirely on providing the searcher what they are looking for. You will be using these pages for your link building campaigns as the URLs for external links to help these pages rank high in the SERPs. You will do a lot of internal linking to these pages. They populate the menus on your site and get interlinked from other relevant articles that you write.
With so many links pointing to these pages you will be sending a lot of pagerank to your evergreen content. You need pagerank to get the page to rank high in the SERPs, but it is also valuable for getting other pages on your site to rank as well. Quality evergreen content will contain links to more focused articles on your site. This allows readers to drill down further into your content for more information about a specific topic and allows you to flow some of that pagerank down to that content.
The more useful your evergreen content is the more external links you will get to these pages. If you create a great resource that addresses a specific need visitors will be more likely to bookmark, share, link to and reference your material.
How to Create It
When creating evergreen content remember that you want to go in-depth on your topic. You want to specifically address a keyword phrase that users will be entering and solve the problem they are gathering information on with their search. The better your page at answering the user's question the more it is going to help you attract links, increase your traffic, and get subscribers or customers.
If you are creating a new site then you should have already picked your niche. Once you pick your niche you drill down a little bit and form categories. Instead of spreading your content out into each category, pick one to start with and really go in-depth. Then combine that content into one useful resource page and use internal links to drill down to the specifics.
For those of you out there who have an established site or blog, you already have content. If you are using categories, start with your most important or the one you have written the most about. Group those articles together. Do some keyword research to find a relevant high traffic keyword that matches your topic and use that to build your evergreen content page.
At a bare minimum you will want a quality introduction followed by a list of internal links that point to more specific information that you have already written. As you are piecing together your page you might find a gap in your content- a specific topic that hasn't been addressed. If you do, the good news is that you have some great new content ideas for what to write about. These evergreen pages are a great place to archive your most important content.
If you are still stuck on what to write about for your evergreen pages, try working on tutorials, how-to's, or answering specific questions. With tutorials or how-to's you can go step-by-step and include pictures. If you answer a specific question a potential customer in your niche might ask you not only have an idea for a great piece of content, but a page that will convert those visitors into buyers.
Cost
Since they will provide you long term benefits you want to make sure these articles are your highest quality content. These pages might be longer or require more expertise than short term content. Do not worry if you do not rank highly for these terms right away since it is not likely they will become outdated.
You will likely pay more to have this content written or use up more of your own time. You just have to compare the benefits of receiving traffic from a page for more than a year, or how much traffic you will receive in a short period of time from your short term content.